Hydrothermal optimal power flow based on hydrothermal decomposition and coordination

This paper presents a novel method for the solution of the hydrothermal optimal power flow problem. The optimization is decoupled into a primary and a secondary stage. The primary stage is a hydrothermal generation scheduling problem. It is decomposed to individual thermal generation scheduling subproblems, one for each time period, and a hydro generation scheduling subproblem, for the whole time horizon. The thermal subproblem is solved by economic generation scheduling using a generalized power balance constraint. The hydro subproblem is solved by network flow programming. The hydrothermal generation scheduling is obtained by a coordination method between the hydro and thermal subproblem solutions. The secondary stage minimizes the power system losses and calculates a feasible solution for each time period. The thermal generators contribute to the loss minimization according to their economic participation factors. This stage is solved by sparse linear programming subject to control-variable step-limit constraints. A carefully designed step-limit control strategy successfully damps the oscillations that are always present in successive linear programming formulations.